Transforming growth factor beta 1 (TGF-b1) induces growth suppression in a variety of cell types. The signaling molecules that are responsible for transmitting TGF-b signal include Smad2, 3, and 4. Upon TGF-b engagement, Smad2 and 3 get phosphorylated and form heteromeric complexes with Smad4 and translocate to nucleus, where in association with transcriptional co-activators or repressors, binds to the promoters of TGF-b-responsive genes. We are studying a diffuse large B-cell lymphoma cell line, DB, that lacks TGF-b responsiveness with respect to growth suppression. Our goal is to identify the deficit(s) in TGF-b signaling pathway in DB cells. Preliminary data indicate that there is a deficit in the nuclear translocation of Smad3 upon TGF-b treatment, while the nuclear translocation of Smad2 is intact. Ectopic expression of wild type Smad3 is being tested to reverse the deficit in TGF-b responsiveness. If the wild type Smad3 is able to reverse the deficit, we will try to sequence the endogenous Smad3 to look for any mutation(s). On the other hand, if we are unable to reverse the deficit with the ectopic expression of Smad3, we will investigate the mechanism of nuclear translocation of Smad3.